Hi Laura,
Yes, resin will work well for this purpose. Before you pour resin, you will want to make sure your piece is dry. I generally like to let glue and paint dry for at least 12 hours. You may even want to wait a couple of days. You may also want to seal the sides and underside of your piece with masking tape as resin will run through any cracks or holes.
The resin will self-level to a depth of approximately 1/16″ to 1/8″. I would suggest pouring one layer, see how you like it, then decide if you want a second layer. It will cure to a glossy finish and look like glass.
As for resin, the Resin Obsession artwork resin will work great. You can buy it in our store here: https://shop.resinobsession.com/collections/resin/resin-obsession-artwork-resin
This blog post may help you as well: https://www.resinobsession.com/resin-tutorials/how-to-apply-a-glossy-resin-layer-to-a-painting It shows how to resin a painting along with an example of how to calculate how much resin you need.